Restrict max packet size on rx

Restrict max packet size on rx

[Rajasekhar Pulluru]

[-- Attachment #1: Type: text/plain, Size: 509 bytes --]

Team,
Does setting mtu using rte_eth_dev_set_mtu limit the maximum size of the
packet received on the dpdk port to the configured mtu size?

On an intel machine with ixgbe port, with mtu set to 1500, no rx-offloads
enabled, ixgbe dpdk port is able to receive packets greater than 1500 size
and even jumbo frames of size 9000, even though the peer is sending them
fragmented with mtu of 1500.

How do I restrict the port not to receive any frame greater than mtu size?

Appreciate any help,
Thanks.
Rajasekhar

[-- Attachment #2: Type: text/html, Size: 635 bytes --]

Re: Restrict max packet size on rx

[Stephen Hemminger]

On Fri, 18 Oct 2024 22:05:24 +0530
Rajasekhar Pulluru <pullururajasekhar@gmail.com> wrote:

> Team,
> Does setting mtu using rte_eth_dev_set_mtu limit the maximum size of the
> packet received on the dpdk port to the configured mtu size?
> 
> On an intel machine with ixgbe port, with mtu set to 1500, no rx-offloads
> enabled, ixgbe dpdk port is able to receive packets greater than 1500 size
> and even jumbo frames of size 9000, even though the peer is sending them
> fragmented with mtu of 1500.
> 
> How do I restrict the port not to receive any frame greater than mtu size?
> 
> Appreciate any help,
> Thanks.
> Rajasekhar


In networking, MTU and MRU are overlapping concepts.
The MTU value is used as a hint to the driver as to what size buffer to allocate
but it can use larger if it wants. If you have restrictions, then the application
needs to enforce them.

Re: Restrict max packet size on rx

[Rajasekhar Pulluru]

[-- Attachment #1: Type: text/plain, Size: 1061 bytes --]

Thanks Stephen.

On Fri, Oct 18, 2024 at 10:13 PM Stephen Hemminger <
stephen@networkplumber.org> wrote:

> On Fri, 18 Oct 2024 22:05:24 +0530
> Rajasekhar Pulluru <pullururajasekhar@gmail.com> wrote:
>
> > Team,
> > Does setting mtu using rte_eth_dev_set_mtu limit the maximum size of the
> > packet received on the dpdk port to the configured mtu size?
> >
> > On an intel machine with ixgbe port, with mtu set to 1500, no rx-offloads
> > enabled, ixgbe dpdk port is able to receive packets greater than 1500
> size
> > and even jumbo frames of size 9000, even though the peer is sending them
> > fragmented with mtu of 1500.
> >
> > How do I restrict the port not to receive any frame greater than mtu
> size?
> >
> > Appreciate any help,
> > Thanks.
> > Rajasekhar
>
>
> In networking, MTU and MRU are overlapping concepts.
> The MTU value is used as a hint to the driver as to what size buffer to
> allocate
> but it can use larger if it wants. If you have restrictions, then the
> application
> needs to enforce them.
>

[-- Attachment #2: Type: text/html, Size: 1491 bytes --]

Re: Restrict max packet size on rx

[Stephen Hemminger]

On Fri, 18 Oct 2024 22:19:35 +0530
Rajasekhar Pulluru <pullururajasekhar@gmail.com> wrote:

> Thanks Stephen.
> 
> On Fri, Oct 18, 2024 at 10:13 PM Stephen Hemminger <
> stephen@networkplumber.org> wrote:  
> 
> > On Fri, 18 Oct 2024 22:05:24 +0530
> > Rajasekhar Pulluru <pullururajasekhar@gmail.com> wrote:
> >  
> > > Team,
> > > Does setting mtu using rte_eth_dev_set_mtu limit the maximum size of the
> > > packet received on the dpdk port to the configured mtu size?
> > >
> > > On an intel machine with ixgbe port, with mtu set to 1500, no rx-offloads
> > > enabled, ixgbe dpdk port is able to receive packets greater than 1500  
> > size  
> > > and even jumbo frames of size 9000, even though the peer is sending them
> > > fragmented with mtu of 1500.
> > >
> > > How do I restrict the port not to receive any frame greater than mtu  
> > size?  
> > >
> > > Appreciate any help,
> > > Thanks.
> > > Rajasekhar  
> >
> >
> > In networking, MTU and MRU are overlapping concepts.
> > The MTU value is used as a hint to the driver as to what size buffer to
> > allocate
> > but it can use larger if it wants. If you have restrictions, then the
> > application
> > needs to enforce them.
> >  

There are some drivers like ixgbe that need to round up the receive buffer to
a power of 2. So it is possible to get 2K frames even with standard 1500 byte MTU.